The present invention relates to a pulse arc welding machine. More specifically, the invention relates to a base current supplying source for a welding machine.
A conventional welding machine of this general type is shown in FIG. 1, in which reference numerals 1 and 2 designate a pulse current supplying source and a base current supplying source, respectively, the output terminals of which are connected in parallel and coupled to an arcing region (described later), 3 a consumable electrode wire, 4 a base material, and 5 an arcing region between the wire 3 and the base material.
FIGS. 2A-2C are graphs of the currents in the arcing region 5 in the welding machine in FIG. 1. The pulse current supplying source 1 operates to supply an electric current as shown in FIG. 2A. This current has a high peak value. During the pulse duration (Tp in FIG. 2A), the end portion of the wire 3 is melted and shifted onto the base material 5 to perform the welding operation. During the pause period (T.sub.B in FIG. 2A), no current is supplied, and therefore it is impossible to maintain the arcing. That is, the arc is cut off, as a result of which the welding is unsatisfactory. In order to eliminate this difficulty, it is necessary to maintain the arcing even during the pause period. In order to meet the requirement, the base current supplying source 2 is connected in parallel to the pulse current supplying source 1 so that an electric current larger than that necessary for maintaining arcing in the arcing region 5 is supplied. With this arrangement, in addition to the base current, a current of high peak value is supplied by the pulse current supplying source 1, as shown in FIG. 2C, in order to maintain arcing so that, with the wire 3 set apart from the base material 4, the end portion of the wire is maintained molten and with the molten metal being shifted onto the base material 4.
FIG. 3 is a circuit diagram showing the welding machine in FIG. 1 more specifically. In FIG. 3, a circuit section 1, indicated by a one-dot chain line, corresponds functionally to the pulse current supplying source 1 in FIG. 1, and a circuit section 2 indicated by a dashed line to the base current supplying source 2. Further in FIG. 3, reference numerals 3, 4 and 5 designate a consumable electrode wire, an arcing region and a base material as in FIG. 1. Reference numeral 6 denotes a primary winding of a transformer; 7 an insulated secondary winding of the transformer; 8, 9 and 10 phase control elements connected to the balanced taps of the secondary winding 7; 11 a phase control element connected to the unbalanced taps of the secondary winding 7; and 12 an inductive element serving as a reactor for suppressing high voltage transients caused by abrupt changes of current. The base current value can be controlled by the ignition phases of the phase control elements 8, 9 and 10, and the pulse current value can be controlled by controlling the ignition phase of the phase control element 11.
As is apparent from FIGS. 1 and 3, the conventional pulse arc welding machine requires in addition to the pulse current supplying source 1 a second, entirely independent current source. That is, the welding machine requires the base current supplying source 2 besides the pulse current supplying source 1. Accordingly, the conventional pulse arc welding machine is disadvantageous in that it has an intricate construction and high manufacturing cost.
Furthermore, the conventional welding machine suffers from the difficulty that, since the repetition frequency of the pulse current is affected by the frequency of the power source, the range of welding current in which the optimum molten droplet transfer state can be obtained is limited, and sometimes it is difficult to employ the welding machine for welding specific materials.
In addition, in the conventional welding machine, although the mean value of the pulse current can be controlled, the instantaneous value thereof cannot be controlled. Therefore, the conventional welding machine suffers from the difficulty that if the arc load is varied, the instantaneous molten droplet transfer state is not uniform.